The use of DC to DC converters for converting a source of direct current (DC) from one voltage level, for example as supplied by a battery, to a another voltage level, for example as required by a particular electronic circuit, is well known. In particular, switch-mode DC to DC converters are well known that convert one DC voltage level to another by storing energy temporarily, and then releasing the stored energy to the output at a different voltage level. The storage of the energy may be in either magnetic field storage components (e.g. inductors, transformers, etc.) or electric field storage components (e.g. capacitors). Such switch-mode DC to DC conversion is more power efficient than linear voltage regulation, and thus switch-mode DC to DC converters are typically more suitable for use within battery operated devices.
Within the automotive industry, DC to DC converters are used to convert, for example, a first voltage level supplied by the vehicle battery to a second voltage level required by one or more electronic components operating within the vehicle. Such DC to DC converters are required to be able to cope with a wide input voltage range due to variations in the voltage supplied by the battery, as well as transient voltages that may be experienced, for example as a result of a ‘load dump’. A load dump may occur, for example, upon the disconnection of the vehicle battery from the alternator while the battery is being charged. As a result of such a disconnection, other loads connected to the alternator (e.g. the DC to DC converter) may experience a power surge resulting in a significantly increased voltage level. Thus, a typical input voltage range that such a DC to DC converter is required to operate across may be, say, between 5 v and 40 v.
The requirements for the next generation of single board computers (SBCs), such as are used within the automotive industry, are currently being defined. In particular, these requirements include several requirements that affect DC to DC converter performance needs when used within the SBCs. Such requirements for the DC to DC converters include: maximum power dissipation; overall efficiency, dynamic response, output voltage ripple, etc.
Known DC to DC converters use various control methods, such as Pulse Frequency Modulation (PFM), Pulse Burst Modulation (PBM), Pulse Width Modulation (PWM), etc. For example, in the case of PWM mode control, a switching frequency for, say, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) of the DC to DC converter is fixed, whilst the duty cycle is adjusted through a feedback loop. The power dissipation within the switching MOSFET may be expressed as:                (a) Conduction losses, which are primarily dependent upon the ‘ON’ resistance of the MOSFET, the duty cycle and the load current; and        (b) Switching losses, which are primarily dependent upon the input voltage, switching frequency and the load current.        
When such a DC to DC converter experiences a high input voltage, for example as caused by a load dump, the switching power losses increase significantly, requiring the device to be able to dissipate the power lost as, for example, heat. In order to achieve this, the external component of the DC to DC converter must be suitably sized in order to be able to sufficiently dissipate this heat. However, size constraints due to available space, costs, etc, and also the maximum power dissipation and overall efficiency requirements being proposed for the next generation of SBCs, mean that such DC to DC converters are constrained in how they are able to cope with the power losses caused by such high input voltages.
In order to reduce the switching losses during periods of high input voltage, it is necessary to decrease the switching frequency of the DC to DC converter. However, this results in a significant degradation in the dynamic response of the DC to DC converter, and an increase in the output voltage ripple. Such degradation in the dynamic response and increase in the output voltage ripple are not only detrimental to the performance of the DC to DC converter, but also conflict with the ability of the DC to DC converter to comply with the proposed requirements for the next generation of SBCs.